Pretty sure it is the first love possessing an ugly old man. So basically he is having sex with the BODY of an old man. That is why he says "still, it's my first love". Meaning, he was probably like " ugh, this guy is old and ugly, but it's just the body. My first love is in there". That's how I took it.
that reply isn’t correct because ml is pretty much alive. he just getting possessed by that old man ghost who couldn’t pass bcs he didn’t get to have sex while he’s still alive, but since our mc is a shaman, ml looks already took that old man’s figure that’s why he looks like that only to /him/ but he’s normal from anyone else’s perspective tho

I dont get it,the old man is the ghost using the ml's body or the ml is the ghost using the oldman's body????